Polyacetal polymers, which are commonly referred to as polyoxymethylene polymers, have become established as exceptionally useful engineering materials in a variety of applications. For instance, because polyoxymethylene polymers have excellent mechanical properties, fatigue resistance, abrasion resistance, chemical resistance, and moldability, they are widely used in constructing polymer articles, such as articles for use in the automotive industry and the electrical industry.
The mechanical properties of polyoxymethylene molding compositions are one of the reasons for their use in numerous applications. To improve their properties, polyoxymethylene polymers are often provided with additives to adapt the properties for a specific application, for example by using reinforcing fibers or tribological modifiers. For instance, polyoxymethylene polymers have been combined with a tribological modifier for producing polymer compositions well suited for use in tribological applications where the polymer article is in moving contact with other articles, such as metal articles, plastic articles, and the like. These tribological applications can include embodiments where the polymer composition is formed into gear wheels, pulleys, sliding elements, and the like. The addition of a tribological modifier can provide a composition with a reduced coefficient of friction, low frictional noise, and low wear.
In the past, high molecular weight polyolefins have been used to improve the wear resistance of polyoxymethylene resins. For instance, U.S. Pat. No. 5,482,987, which is incorporated herein by reference in its entirety, discloses a self-lubricating, low wear composition containing a polyoxymethylene and a lubricating system comprising a high molecular weight polyethylene, a high density polyethylene, and other components. U.S. Pat. No. 5,641,824, which is incorporated herein by reference in its entirety, discloses a self-lubricating melt blend of a polyoxymethylene and an ultra-high molecular weight polyethylene. A tribologically modified polyoxymethylene polymer composition is also disclosed in U.S. Patent Publication No. 2015/0111796, which is also incorporated herein by reference.
Although polyoxymethylene polymers have been tribologically modified in the past, further improvements are still necessary. For instance, many tribological modifiers for polyoxymethylene polymers are temperature sensitive. Many tribological modifiers either do not work at high temperature or at low temperature. Consequently, a need exists for a tribological modifier for polyoxymethylene polymers that can operate over an extended range of temperatures.
In addition, in many applications, a component made from a thermoplastic polymer is intended to slide against, rub against, or otherwise contact during movement another component also made from a thermoplastic polymer. It is desirable in certain applications for the two components to contact each other without creating noise associated with the stick-slip phenomenon. Noise generation, for instance, is particularly problematic in consumer appliances and other consumer products where noise generation is highly undesirable. Noise generation in these applications is also influenced by the application temperature. Thus, a need also exists for a tribological modifier that can be incorporated into a polyoxymethylene polymer that not only has functionality over a wide temperature range but can also lead to decreased noise generation when contacting another component.